Upgrade elk stack to a more recent version
Last version of grafana doesn't support our old ELK stack anymore:
Support for Elasticsearch versions after their end-of-life (currently versions < 7.10) was removed.
It's now impossible to display a dashboard with queries on ELK. For example: https://grafana.softwareheritage.org/d/ae800PLMk/apache-requests-statistics?orgId=1&inspect=7&inspectTab=error
Migrated from T4455 (view on Phabricator)